Method of infiltrating a metal powder compact



June 20, 1967 c. R. TALMAGE 3,32%,fim

METHOD OF INFILTRATING A METAL POWDER COMPACT Filed Feb. 5, 1964 5 Sheets-Sheet l Ms 6% k g W 5i FIG.

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ATTORNEYS United States Patent 3,326,678 METHOD OF INFILTRATING A METAL POWDER COMPACT Charles Robert Taimage, Bowery Road, New Canaan, Conn. 06840 Filed Feb. 3, 1964, Ser. No. 342,158 4 Claims. (Cl. 752tl8) This invention relates to the method of making sintered metal objects infiltrated with a non-ferrous metal and in particular to the method of making a sintered metal brake track infiltrated with a metal having a high thermal conductivity.

The objects of this invention are to provide a method of making an infiltrated sintered metal part that is economical and efiicient; that reduces the likelihood of fracturing the metal powder compact prior to sintering and infiltrating; and that localizes erosion of the metal powder compact by the infiltrant to areas where the erosion can be tolerated or where the effect of the erosion can be eliminated economically by subsequent machining.

In the drawings:

FIG. 1 shows a brake drum looking into the cavity thereof, the brake drum having a sintered metal powder brake track.

FIG. 2 is an enlarged fragmentary section taken along line 22 of FIG. 1.

FIG. 3 is a fragmentary section illustrating a cylindrical composite compact of metal powder and infiltrant powder together with the steel brake drum shell into which the composite compact is inserted during the making of the brake drum shown in FIGS. 1 and 2.

FIG. 4 is a fragmentary vertical section taken through the tool set of a press which is used to fabricate the composite compact shown in FIG. 3.

FIG. 5 is a fragmentary section of the tool set shown in FIG. 4 to illustrate the step of compacting the metal powder.

FIG. 6 is a fragmentary vertical section taken through the tool set shown in FIG. 4 to illustrate the step of positioning infiltrant powder adjacent the previously compacted metal powder.

FIG. 7 is a fragmentary vertical section taken through the tool set shown in FIG. 4 to illustrate the step of compacting the infiltrant powder in direct contact with the metal powder. I

FIGS. 8, 9 and 10 illustrate a modification in the compacting steps shown in FIGS. 5, 6 and 7.

By way of description and not for purposes of limitation, FIGS. 1 and 2 illustrate a finished brake drum 6 comprising a generally cylindrical steel shell 8, a back 10 and a brake track 12 that lines the inner cylindrical surface 11 of shell 8. Brake track 12 is comprised of sintered ferrous metal infiltrated with copper. The copper also brazes brake track 12 to shell 8 along surface 11. Back 10 may be welded to a radially inward extending flange 14 on shell 8. Back 10 is provided with a central aperture 13 and bolt holes 15 for assembling drum 6 on other Wheel parts. Shell 8 also has an outwardly flared portion 16 that forms a dust seal when drum 6 is assembled with other brake parts.

In accordance with this invention the brake track 12 is fabricated by compacting a composite compact 20 (FIG. 3) comprising a generally cylindrical sleeve 22 of a ferrous powder blend and a generally cylindrical sleeve 24 of copper or copper alloy powder which is compacted in direct contact with the ferrous powder in sleeve 22. A typical ferrous powder blend includes primarily iron powder together with graphite and a suitable lubricant.

Preferably compact 20 (FIG. 3) is fabricated with a press having a tool set of the type illustrated in FIGS.

4-7. The lower tools which are mounted on the bed of a conventional press (not shown) are an outer confining die 30 and a core 32 which is spaced concentrically and radially inward of die 36 to form an annular cylindrical receptacle 34. Receptable 34 is closed at its lower end by an annular punch 36 independently actuated as by a hydraulic cylinder. An annular punch 33 mounted on the ram (not shown) is vertically aligned to register with receptacle 34. With the press open so that die 3% core 32, and punch 38 are spaced apart as shown in FIG. 4, receptacle 34 is filled with a quantity of ferrous powder blend 49 sufficient to form sleeve 22. When the ram is lowered, punch 38 descends into receptacle 34 and compacts powder as into sleeve 22. FIG. 5 illustrates the position of punch 38 at the end of the compacting step. Suitable stops are provided in the press to accurately terminate the descent of punch 38 when powder 44) has been compacted into the proper length for sleeve 22. The ram is then raised to withdraw punch 38 from receptacle 34. A quantity of loose copper or copper alloy powder 46 and suitable lubricant sufiicient to form sleeve 24 is then fed into receptacle 34 in direct contact with sleeve 22 (FIG. 6). The ram is again lowered so that punch 38 compacts copper powder 46 to form sleeve 24 (FIG. 7). Again, suitable stops are provided in the press to limit the down- Ward travel of punch 38 on the second compacting operation. Punch 38 is then withdrawn from receptacle 34 and the compact 20 is ejected from receptacle 34 by upward travel of punch 36.

Preferably compact 20 is assembled within shell 8 (FIG. 3) and the assembly is heated to a temperature of approximately 2050 F. to sinter the ferrous powder in sleeve 22 and melt the copper in sleeve 24. The molten copper infiltrates sleeve 22 and also contacts shell 3 to braze sleeve 22 to shell 8. Alternatively, compact 20 may be heated separately to sinter and infiltrate sleeve 22 before being secured within shell 8.

With the embodiment ilustrated in FIGS. 8, 9 and 10, receptacle 34 is filled with a ferrous powder blend 40 as illustrated in FIG. 4. Punch 38 is then lowered to partially compact powder 4% as designated by numeral 50 (FIG. 8). FIG. 8 shows punch 38 at the lower limit of its vertical travel set by suitable stops in the press. Punch 33 is withdrawn and receptacle 34 is evenly filled to the top with loose copper or copper alloy powder 56 directly on the initial fill of the ferrous powder blend (FIG. 9). The lower limit of vertical travel of punch 38 is set so that receptacle 3 when full, holds the exact quantity of copper powder required to form a sleeve corresponding to sleeve 24. Punch 38 is again lowered into the receptacle 34 and simultaneously punch 38 is raised to compact the powders in receptacle 34 and produce the finished sleeves 58, 60 (FIG. 10) corresponding to sleeves 22, 24 in FIG. 7. Punch 38 may then be raised and the composite compact ejected by further upward travel of punch 36.

Although the fabrication of compact 20 has been described in conjunction with a two-stroke press, it is to be understood that for some applications copper powder and ferrous powder blend may be compacted simultaneouly but in separate compacts or bodies. This is easily accomplished by dimensioning the height of receptacle 34 to accommodate the required quantities of ferrous powder and copper powder sufficient to form the composite compact 20. The required ferrous powder blend is fed into receptacle 34 and then the required copper powder is placed on the initial fill of ferrous powder. Alternately after the required amount of ferrous powder blend has been placed in receptacle 34 punch 36 could be lowered so that receptacle 34 could be refilled with the required amount of copper powder directly on top of the initial ferrous powder blend. A single stroke of either punch 36 or punch 38 can simultaneously compact the copper powder and ferrous powder to form a composite compact similar to compact 20 shown in FIG. 3.

By way of example, in the two-stroke method sleeve 22 may be made from a ferrous powder blend of pure iron with about one percent graphite by weight and one and one-fourth percent lithium stearate (lubricant) by weight. For iron powder sieved through a 100 mesh per inch screen, and a compacting pressure in the order of 30 tons per square inch, about 20 percent copper powder by weight of the ferrous powder blend is used to infiltrate slevee 22 during the sintering opeartion. The amount of copper can be varied depending on the cost of the copper and the extent to which the porosity of the sleeve 22 is to be filled, for example, 100 percent of the porosity down to 25 percent or even less. Depending on the density of the powders, receptacle 34 may have a height in the range of two to two and one-half times the height of sleeve 22 in order to accommodate the powders. The melting temperature of the infiltrant must be within the sintering temperature range of the ferrous powder so that sleeve 22 is simultaneously sintered and infiltrated when it is heated. Properties of the sintered metal combination may be varied by controlling the time-temperature function below the melting point of the infiltrant. For example, by heating the composite compact at a temperature below the melting point of the infiltrant, sleeve 22 can be partially sintered prior to being infiltrated.

When sintered metal articles are manufactured in accordance with the methods described hereinabove, production costs are decreased substantially by a reduction in the number of handling operations previously used to compact and assemble infiltrant powders and ferrous powders. Intimate contact between the infiltrant and ferrous powder during the sintering operation is assure-d and the likelihood of fracturing the ferrous powder compact is reduced. When fabricating sintered metal objects as brake track 12 illustrated in FIG. 1 the infiltrant is compacted at the end of sleeve 22 so that any erosion of the ferrous powder during the combined sintering and infiltrating operation takes place at the end of finished brake track 12 where such erosion can be tolerated and not affect the utility of the brake drum.

The above method which has been described in conjunction with fabricating the composite compact 20 for use in making brake drums is also useful in compacting infiltrants other than copper, for example brass and other non-ferrous alloys, to improve physical properties, such as porosity and mechanical strength, of sintered compacts for applications other than brake drums.

I claim:

1. In the method of making a composite compact of metal powders and infiltrant powders with a press of the type having a die cavity and a compacting punch aligned with said cavity and adapted to be positioned therein, said infiltrant powders having a melting point within the sintering temperature range of said metal powders, the steps of compacting one of said powders in a first portion of said cavity with said punch, retaining said compacted powders in said cavity while said punch is withdrawn, compacting the other of said powders in a second portion of said cavity with said punch, said second portion of said cavity being directly adjacent said first portion of said cavity so that said other powders are compacted in direct intimate contact with said one powder to form a composite compact, removing said composite compact from said cavity, and then heating said composite compact at a temperature within a range that will sinter said met-a1 powders and melt said infiltrant powders.

2. In the method of making a brake drum having a sleeve-like sintered metal brake track with an inner surface of said track providing a friction braking surface, the steps of compacting first powders to form a first sleeve, compacting second powders onto said first sleeve in direct intimate contact with said first powders to form said second powders into a second sleeve and substantially simultaneously form said first and second sleeves into a unitary composite compact, one of said powders being ferrous powders and the other of said powders being infiltrant powders having a melting temperature within the sintering temperature range of said ferrous powders, said infiltrant powders being arranged and disposed while the sleeves are compacted together so that direct intimate contact between said ferrous powders and said infiltrant powders is located other than at a surface of said ferrous powders sleeve corresponding to said braking surface of a finished brake drum, and said method further comprises heating said composite compact to a temperature within said temperature range to sinter said ferrous powders and melt said infiltrant powders to thereby infiltrate said ferrous powders whereby any erosion and pitting of said ferrous powders during infiltration is located other than at said braking surface.

3. The method set forth in claim 2 wherein said infiltrant powders are compacted as an axial extension of said ferrous powders sleeve with direct intimate contact between said infiltrant powders and said ferrous powders at an end face of said ferrous powders sleeve.

4. The method of making a sintered metal article infiltrated with an infiltrant comprising compacting metal powders into a compact having a contour generally corresponding to the contour of said article, compacting infiltrant powders in direct intimate contact with a predetermined surface portion of said metal powders compact to form a composite compact with the contour of said metal powders compact conforming closely to the contour of a finished article, said infiltrant powders having a melting temperature within the sintering temperature range of said metal powders, and then heating said composite compact at a temperature in a range that will sinter said 'metal powders and melt said infiltrant powders whereby any pitting and erosion of the sintered metal powders compact caused by infiltration is localized at said predetermined surface portion.

References Cited UNITED STATES PATENTS 1,910,884 5/1933 Comstock -201 K 2,287,952 6/ 1942 Tormyn.

2,350,971 6/1944 Pecker et al 75208 X 2,357,407 9/1944 Kurtz 2641 11 2,401,221 5/1946 Bourne 29-1822 X 2,422,439 6/ 1947 Schwarzkopf 75208 2,696,434 12/1954 Bartlett 75208 2,715,589 8/1955 Smith 75208 X 2,778,742 1/ 1957 Shipe.

2,873,517 2/1959- Wellman 29420.5

FOREIGN PATENTS 369,964 3/1932 Great Britain.

OTHER REFERENCES Powder Metallurgy: Schwartzkopf, New York, Mac- Millan Co., 1947.

CARL D. QUARFORTH, Primary Examiner.

REUBEN EPSTEI'N, L. DEWAYNE RUTLEDGE,

Examiners. R. L. GRUDZIECKI, Assistant Examiner, 

2. IN THE METHOD OF MAKING A BRAKE DRUM HAVING A SLEEVE-LIKE SINTERED METAL BRAKE TRACK WITH AN INNER SURFACE OF SAID TRACK PROVIDING A FRICTION BRAKING SURFACE, THE STEPS OF COMPACTING FIRST POWDERS TO FORM A FIRST SLEEVE, COMPACTING SECOND POWDERS ONTO SAID FIRST SLEEVE IN DIRECT INTIMATE CONTACT WITH SAID FIRST POWDERS TO FORM SAID SECOND POWDERS INTO A SECOND SLEEVE AND SUBSTANTIALLY SIMULTANEOUSLY FORM SAID FIRST AND SECOND SLEEVES INTO A UNITARY COMPOSITE COMPACT, ONE OF SAID POWDERS BEING FERROUS POWDERS AND THE OTHER OF SAID POWDERS BEING INFILTRANT POWDERS HAVING A MELTING TEMPERATURE WITHIN THE SINTERING TEMPERATURE RANGE OF SAID FERROUS POWDERS, SAID INFILTRANT POWDERS BEING ARRANGED AND DISPOSED WHILE THE SLEEVES ARE COMPACTED TOGETHER SO THAT DIRECT INTIMATE CONTACT BETWEEN SAID FERROUS POWDERS AND SAID INFILTRANT POWDERS IS LCOATED OTHER THAN AT A SURFACE OF SAID FERROUS POWDERS SLEEVE CORRESPONDING TO SAID BRAKING SURFACE OF A FINISHED BRAKE DRUM, AND SAID METHOD FURTHER COMPRISES HEATING SAID COMPOSITE COMPACT TO A TEMPERATURE WITHIN SAID TEMPERATURE RANGE TO SINTER SAID FERROUS POWDERS AND MELT SAID INFILTRANT POWDERS TO THEREBY INFILTRATE SAID FERROUS POWDERS WHEREBY ANY EROSION AND PITTING OF SAID FERROUS POWDERS DURING INFILTRATION IS LOCATED OTHER THAN AT SAID BRAKING SURFACE. 